api!: remove default value for "addr" config

"addr" is already deprecated and its default value was using "configured_addr".
We want to get rid of "configured_addr" too, but users should at least
not access it through deprecated config.

src/config.rs

@@ -549,7 +549,6 @@ impl Context {
         // Default values
         let val = match key {
             Config::ConfiguredInboxFolder => Some("INBOX".to_string()),
-            Config::Addr => self.get_config_opt(Config::ConfiguredAddr).await?,
             _ => key.get_str("default").map(|s| s.to_string()),
         };
         Ok(val)